The present invention relates generally to a voltage stability monitoring and control system/scheme, and more particularly to a system and a method for determining voltage stability margin at load centers to enhance power system voltage stability monitoring and control capability.
A load center is generally defined as a particular geographical area where load demand is high and has few local power plants to satisfy the local power demand. Because there are few local power plants to satisfy the demand, the load center is usually supplied by multiple transmission sources through a number of boundary buses, resulting in a high proportional amount of load demand being provided by external power systems and heavy power flow on the interface transmission lines.
Because of these properties, load centers are more susceptible to voltage instability and are typically voltage weak areas. Therefore, monitoring voltage stability at load centers is important and necessary. By monitoring the voltage stability condition at load centers and taking timely control actions, voltage instability can be effectively limited in its own area without expanding to the rest of the system.
One way to monitor and control voltage stability is by using Under Voltage Load Shedding (UVLS) schemes. UVLS schemes have been used in power systems as an economic means of avoiding voltage collapse. Voltage magnitude is used as triggering criteria in most of the UVLS schemes. As such, UVLS schemes shed load in pre-defined blocks that are triggered in stages when a local voltage drops to pre-defined levels. Voltage Instability Load Shedding (VILS) schemes have also been used to enhance conventional UVLS schemes. VILS schemes calculate the critical voltage and voltage stability margin continuously at a local bus using measured voltage and current waveforms.
Unfortunately, both UVLS and VILS schemes are only designed to monitor and control voltage stability at local buses, and are not competent to monitor and control voltage stability at load centers.